1. Field of the Invention
The present invention relates to an anti-fogging coating composition used on a support for forming an anti-fogging, mechanically resistant film, a product bearing said film, whose surface has an anti-fogging character,-and a method for preparing said product.
2. Background of the Art
Numerous supports, such as plastics and glass, have the disadvantage of becoming fogged when their surface temperature falls beneath the dewpoint of the surrounding air. This is particularly true of the glass which is used to form glazings for transportation vehicles or buildings, optical glasses, lenses, mirrors, etc. The formation of fog on these surfaces causes a decrease in transparency due to diffusion of light by drops of water, which can be highly bothersome.
In order to prevent the formation of fog, that is the condensation of fine droplets of water on a support, the deposit of hydrophilic layers has been proposed. Thus, German Patent DE 1 928 409 describes an anti-fogging coating formed of hydroxyalkyl acrylate or methacrylate polymers. These very hydrophilic layers absorb water and provide the formation, in the presence of excess water, of a film of water on the surface which does not impede transparency. However, these layers, through the absorption of water, swell, soften and becomes less mechanically resistant.
Crosslinking these layers improves their mechanical resistance, but their anti-fogging property, that is the ability to absorb the water over the entire surface of the support, decreases.
To compensate for the harmful effect of the crosslinking on the anti-fogging character, it has been proposed, as described in French Patent 2 253 075 for example, to add tensio-active agents.
However, research has continued to find compositions for anti-fogging coating from which, using processes which are easily carried out, layers can be formed whose anti-fogging and mechanical resistance properties are lasting.